1. Field of the Invention
The present invention relates to a substrate processing apparatus and a substrate processing method for performing a series of processes on semiconductor substrates, glass substrates for liquid crystal displays, glass substrates for photomasks, substrates for optical disks and the like (hereinafter simply referred to as “substrates”), and it more specifically relates to improvement in control of substrate transport.
2. Description of the Background Art
A substrate processing apparatus may require time to control processing environment in a certain processing unit.
A heating unit in a substrate processing apparatus serves for heating of substrates. As an example, when two or more lots require different processing temperatures for heating and substrates in each lot are all to be subjected to heating, the processing temperature in the heating unit should be adjusted between the lots. As a particular example, when one lot requires a temperature of 65° C. for heating whereas a subsequent lot requires a temperature of 75° C., the processing temperature in the heating unit should be raised after heating of the last substrate in the previous lot is finished.
If the substrates in the subsequent lot are carried into the heating unit without waiting for sufficient rise of the processing temperature, processing temperature for heating differs between substrates at the beginning of the subsequent lot and other substrates of the same lot after temperature adjustment, thus producing a mixture of substrates with different characteristics in the same lot.
A tact transport control system serves to prevent such a problem in which substrate transport is controlled on the basis of tact time (the time interval between start of a substrate process at a certain processing part and start of the same process on a subsequent substrate at the same processing part). An example of this control system is introduced in Japanese Patent Application Laid-Open No. 4-113612 (1992). In this publication, standby time until a substrate is carried into a processing unit and tact time are controlled so that substrates are provided with uniform processing, even in a transition period required for change of a processing environment.
A sequential transport control system for sequentially transporting a plurality of substrates with minimum possible interruption with no dependence on tact time has no concept of time-base control such as control depending on standby time or tact time. That is, the sequential transport control system cannot control time interval and timing in substrate transport, and hence, stop of transport may be the first policy in the necessity for standby of substrate transport. By way of example, in the event that the sequential transport control system encounters the foregoing necessity of adjusting processing temperature in a heating unit between lots, the system makes an indexer (serving to receive unprocessed substrates, to feed unprocessed substrates to the processing apparatus, and to transfer processed substrates to the outside) stop feed of substrates into the processing apparatus.
Such a course of action is introduced in FIG. 15 which shows an exemplary transport path and exemplary locations of substrates in a substrate processing apparatus. With reference to FIG. 15, a substrate passes an indexer ID, an adhesion processing unit (discussed below) AHL, an anti-reflection film processor ARC, a heating plate HP1, a heater PHP1 as a heating unit, a photoresist spin coater SC, cooling plates CP1 and CP2, and a substrate holding part PASS3 in a predetermined order which together form the transport path.
It is assumed that a substrate Wb in one lot is being subjected to heating at the heater PHP1 in the substrate processing apparatus, and the heater PHP1 is to change its processing temperature thereafter. The sequential transport control system sequentially transports substrates with minimum possible interruption. Therefore, when a substrate in a subsequent lot exists in the photoresist spin coater SC as an ante-stage of the heater PHP1, this substrate in the subsequent lot is carried from the photoresist spin coater SC into the heater PHP1 prior to completion of the change of the processing temperature, thus producing a mixture of substrates with different characteristics in the same lot as discussed.
In response, transport of a substrate Wa in the subsequent lot that requires change of the processing temperature is held in standby without being fed from the indexer ID as shown in FIG. 15. At the time when the change of the processing temperature is completed in the heater PHP1, transport of substrates is restarted from the indexer ID.
Suspension of transport in this manner puts substrate transport on hold until feed is restarted, which inevitably causes throughput reduction.